Tundras may have emerged when the ecosystem services from megafauna ceased due to too successful hunting by humans. Today, thawing tundras threaten to release their trapped methane and accelerate climat change. But some believe that there is a remedy: restored grasslands, repopulated by grazing animals. Perhaps even mammoth hybrids?

Herds of mammoths and wild horses, mastodons, aurochs and bison; during the pleistocene era (between two million years and about ten thousand years ago) a grazing megafauna dominated the landscapes and safeguarded open spaces. Towards the end of the period, most of the megafauna was lost. The landscape changed and great forests returned.

What happened? The popular hypothesis has long been climate change; that the ecosystems were destabilized by the rising temperatures, causing the plains to be replaced by forests and tundras, in turn causing famine among the large mammals. The russian geophysicist Sergey Zimov has a different opinion, however: he believes that the animals were lost first, to a large extent hunted to extinction by the modern man, who was then extending his dominion across the globe. The mammoth, for instance, had thrived on the Northern Hemisphere for millions of years when humans arrived on the scene. Ten thousand years ago, they were pushed back to a few areas in what is now Sibiria. The last one died some 4 000 years ago. In northern Asia, 8 species of megafauna disappeared when humans arrived. In North America: 33. In South America: more than 50.

Just 15 000 years ago, most of the planet’s land mass was covered by pastures; forests only occurred on patches of less fertile land. In this ecosystem of pastures, large grazing mammals amounted to 1.6 billion tonnes of biomass.

Homo Sapiens eradicated half of the large animals on the planet before even inventing the wheel, writing or iron tools”, writes the historian Yuval Noah Harari.

According to estimates based on bone findings, the grasslands contained ten tonnes of animals per square kilometer. The megafauna rooted the soil, trampled and fertilized it. But when they disappeared, those ecosystem services disappeared with them; according to Zimov, that is what caused the landscape to transform.

The time bomb of climate change

Almost a quarter of the soil on the Northern Hemisphere is frozen all year round. Vast amounts of land are in the grip of this permafrost, and hidden within lies an abundance of carbon and methane from ancient vegetation: more than twice the amount in the current carbon cycle. The problem is that global warming is causing the permafrost to thaw. This could cause a positive feedback loop to form, where the release of trapped greenhouse gases accelerate the warming, in turn causing the tundra to thaw even faster – and so on.

Since 1989, Sergey Zimov is busy working on a research project in Sibiria: the Pleistocene Park. It is a large enclosure on the tundra, where reindeer, muskoxen and many other animals are gathered in hope that their presence will be able to de-shrub the tundra and restore the former grassland. Zimov believes that it will be enough to fill up the ecosystem with animals that are capable of living there, and that the transformation will follow.

”There is an increasing amount of studies strongly suggesting that humans played an important role in the extinction of the Pleistocene megafauna”, says Joris Cromsigt, ecologist at the Swedish University of Agricultural Sciences and Utrecht University. He continues:

In 2018, a 40 000 year old mammoth rib was discovered in Russia, with an ivory arrowhead embedded in the bone. This proves that humans actively hunted mammoth at the time.

”Work from Sweden is actually supporting the hypothesis that grasslands could be restored. Johan Olofsson et al at Umeå University show that intense reindeer use can shift shrub tundra to grassland steppe.”

There are other examples as well. When a vulnerable population of gnus in the Serengeti started to recover, the trampled soil became more fertile, the vegetation increased, there were fewer fires, and the land turned into a carbon sink.

Grasslands could stop the thawing

But why the urge to restore the grassland steppes? Because, according to Zimov, that is the way to halt the release of methane from the thawing permafrost. The grass cover would brighten the ground, causing an albedo effect so that it absorbs less heat from the sun. It would also insulate the soil, and prevent it from thawing in the summer. In the winter, on the other hand, the rooting animals would break through the otherwise insulating snow and allow the cold to reach deeper into the ground. And according to his results, the hypothesis holds: a couple of feet down in the ground, the temperature is definitely lower inside the park than outside.

Thawing permafrost can cause entire layers of soil to collapse, along with the surface vegetation.

”It is not unlikely that the mechanisms could prevent permafrost loss in the way Zimov suggests, and again empirical work by Olofsson et al and others provide support for the mechanisms at small scale. The key question, of course, is whether it will be feasible to build-up large enough populations of megafauna across large enough areas to have a significant effect”, Joris Cromsigt says.

Which species would be the best candidates for a modern megafauna, then? In lack of the extinct pleistocene species, the best bet would be to find species that operate in similar niches.

”The broader concept of trophic rewilding deals with conserving and rebuilding the populations of current large mammals to restore their functional roles. Pleistocene rewilding deals with restoring Pleistocene ecosystems and using extant functional equivalents to do this. E.g., use African forest elephant as the functional equivalent of similar extinct Pleistocene species in North America and Europe – and thus bring African forest elephant to North America and Europe as substitute for the extinct Pleistocene species”, Joris Cromsigt explains.

Elephant-mammoth hybrides on the tundra?

An ongoing project called Revive & Restore is attempting to do this in its most extreme form. The idea is to edit the genome of extant elephants, in order to give them features which would help them cope with the climate in the North – and these would be extracted from the genome of the woolly mammoth. The upgrades the project is aiming for are primarily climate adaptations such as a long, dense fur and insulating subcutaneous fat. Such an elephant-mammoth hybrid could then be released to graze on the restored pleistocene-like grassland steppes, where it would occupy a special niche.

”It will for sure be special! I am actually not a big proponent of focusing on bringing back the mammoth or other extinct species. We have a lot of opportunities still with extant megafauna, like the ones Zimov is using in his project (reindeer, bison, musk oxen, przewalski horse). I think we should focus on try to restore what we still have”, Joris Cromsigt says.

Positive climate impact from rewilding

In a recent peer-reviewed article, Joris Cromsigt et al demonstrated that active measures to increase the number of large mammals in an area – so-called rewilding measures – have the potential to increase carbon uptake, and hence would counter the global warming in other ways as well. Very large animals are especially important:

”I think this is a powerful example. Simply said: in large parts of the tropics tree species with the hardest wood store the most carbon for the longest period of time. These species also depend on megafauna for their dispersal and recruitment. By benefiting these tree species, megafauna thus facilitate carbon storage”, Joris Cromsigt says.

Our contemporary farm animals produce more methane than the wild species of megafauna. This means that reducing the number of livestock and increasing the number of wild animals could be another possible future climate intervention.

”We do not say this should be done, but that it could be done – as one alternative future scenario of using the earth more sustainably, in a more climate-smart way. The core condition here is that people very seriously cut down their meat consumption. Say max one times per week, and in small portions. The land that is then freed up because it’s no longer needed to feed livestock could be allocated to wildlife, which could be harvested sustainably for meat consumption. There are also all kinds of scenarios in between where use of wild meat is mixed with livestock meat”, Joris Cromsigt says.

Meanwhile in Russia, a freezing cold winter encapsulates tens of millions of hectares. Five meters below ground, the temperature is 0.9°C warmer compared to ten years ago. And in a Harvard laboratory, researchers are looking for the next mammoth gene to add to the 40 or so already isolated.

The article was published in January 2019.